I. Field of the Invention
The present invention relates to optical scanning and reading equipment and, in particular, to systems for scanning a light beam across a target such as a bar code symbol.
II. Description of the Related Art
In a light beam scanner, a small spot of light is swept rapidly across a target such as a bar code symbol. After reflection from the target, a photoelectric converter such as a photo diode detects the reflected light and converts it to electronic signals representing features of the target. A bar code scanner is an important commercial application for beam scanners and is referred to herein as a typical example of a specific application for the present invention.
Various mechanisms exist in the prior art for sweeping (or scanning) a light beam across a target. One such prior art mechanism is shown in FIG. 9. In the mechanism of FIG. 9, a coil 145 wound on bobbin 146 is attached to a steel mounting frame 148. Steel rivets with heads 147a and 147b act as poles for coil 145. A scan element 149a has a fixed end 149b mounted to mount 149 which in turn is fastened to a scanner chassis. The scan element 149a is a laminated structure made from flexible copper clad printed circuit stock. The laminated structure at the fixed end has copper layer 133 laminated to flexible plastic film 135 (e.g. polyamide film) also laminated to copper layer 136 which is in turn affixed to mounting bracket 149. The flexible end 149c of the scan element includes copper layer 131 laminated to film layer 135 which in turn is laminated to copper layer 138. Flexible film layer 135 holds the fixed end 149b and the flexible end 149c of the scan element together.
The scan element shown in FIG. 9 includes an open area 137 that is formed by etching away a portion of copper between layer sections 138 and 136. The area immediately above area 137 is also been formed by etching the copper away between copper layer sections 133 and 131 and back filling this area with an elastomer fill 132. Mirror 134 is attached to copper layer 131 and magnet 140 is attached to copper layer 138. Magnet 140 causes mirror 134 to dither in the direction of double arrow 139 when acted upon by current introduced into coil 145. In the scan mechanism of FIG. 9, film layer 135 is a permanent part of the structure and is substantially thick (i.e., on the order of 0.030xe2x80x3) imparting stiffness to the flexural characteristics of the device. Since film layer 135 acts as a stiffening layer, this structure must be made relatively large and heavy in order to achieve slow scan rates on the order of 20 Hz. Furthermore, the stiffening effect of plastic layer 135 reduces the Q of the system and acts as a damper so that many oscillations cannot be maintained by the introduction of only a single current pulse in coil 145. As described more fully below, one object of the present invention is to overcome this problem by providing a scan system wherein sufficient oscillations can be maintained by introduction of only a single current pulse in the drive coil or by application of some other momentary distortion force to the system.
Due to the relatively high rigidity of film layer 135, coil 145 must be large with an iron core having pole faces to sufficiently act upon magnet 140. Furthermore, mass manufacture of the device of FIG. 9 requires a significant number of steps and components. As described more fully below, it is a further object of the present invention to provide a scan system which does not require such a large coil and which can be mass manufactured more easily and cost efficiently than the mechanism of FIG. 9.
U.S. Pat. No. 4,593,186 entitled xe2x80x9cPortable Laser Scanning System and Scanning Methodsxe2x80x9d discloses a portable laser scanning system for reading bar code symbols. The system includes means for generating and directing a laser beam, scanning means for scanning the laser beam across a symbol, sensor means for detecting light reflected from the symbol and generating a signal, signal processing means for processing the signal, decoding means for decoding the signal, manually actuatable trigger means for initiating each reading of the symbol, power supply means, and means for determining a successful decoding of each symbol and for non-manually terminating the reading of each symbol after a successful decode. Alternatively, the system includes means for determining that a symbol has not been successfully decoded and for non-manually terminating the reading of the symbol if the symbol has not been successfully decoded after a predetermined amount of time. Thus, in the system of the ""186 patent, the deactuation of the scan system depends, at least in part, on a determination as to whether a symbol has been successfully decoded. In the present invention the determination as to whether the symbol has been successfully decoded or not is not necessary in order to properly and efficiently deactuate a scanning system. It is thus an object of the present invention to provide an improved and simpler sequence for actuating and deactuating the elements in a scan system which functions independently of any determination that the symbol has been successfully or unsuccessfully decoded. In doing so the benefits are significant, among these are: less battery energy needed, easier to use, fewer components needed, lower assembly costs, less space required to mount the scanner and quicker scan sequences.
The scan systems disclosed in the ""186 patent also include motors that must be supplied power continuously during the entire scan sequence. To conserve power the motors are shut down in response to, for example, determinations that the symbol has or has not been successfully decoded. As will be explained more fully below, it is a further object of the present invention, to provide an actuation sequence that is more efficient than that described in the ""186 patent, and which does not require continuous power to the scan element during the entire scan sequence.
The present invention is directed to a flexible scan element for scanning a light beam. The scan element includes a first leaf that is rigidly affixed to a substrate, a second leaf having a mirror affixed thereto, and a flexible hinge that couples the first leaf to the second leaf. The second leaf is moveable and pivots about an axis of the flexible hinge. The first leaf is coupled to the second leaf by the flexible hinge which is formed solely from an elastomer material. The first and second leaves are preferably formed from flat rigid metal, and optionally include bonding flanges that couple the leaves to the elastomeric material. The mirror is affixed on one side of the second leaf and a magnet is optionally affixed on the opposite side of the second leaf. The scan element optionally includes tabs for mounting the device to a flat substrate or circuit board, and, in one embodiment has a resonant frequency in the range of 20 Hz-100 Hz.
In accordance with a further aspect, the present invention is directed to a flexible scan element that includes a first leaf that is rigidly affixed to a substrate, a second leaf having a mirror affixed thereto, and a flexible hinge that couples a first end of the first leaf to a first end of the second leaf. The second leaf is moveable and pivots about an axis of the flexible hinge. In accordance with this further aspect, a gap separates the first end of the first rigid leaf from the first end of the second rigid leaf, and the gap has a minimum width that ranges from 3-20 mils. In a particularly preferred embodiment, the gap has a width of about 7 mils.
In accordance with a still further aspect, the present invention is directed to a flexible scan element that includes a first leaf that is rigidly affixed to a substrate, a second leaf having a mirror affixed thereto, and a flexible hinge that couples a first end of the first leaf to a first end of the second leaf. The second leaf is moveable and pivots about an axis of the flexible hinge. In accordance with this further aspect, the flexible hinge may be located within as little as 0.002 inches of the mirror. In alternate embodiments, the distance between the hinge axis and the mirror ranges from 0.003 inches to 0.03 inches.
In accordance with a further aspect, the present invention is directed to a method for manufacturing a flexible scan element. First and second leaves are formed from flat metal such that a gap exists between the first leaf and the second leaf. The first leaf and the second leaf with the gap therebetween are positioned on a flat surface. Next, a flexible hinge is formed in the gap by applying a flowable elastomer to the gap. After the elastomer has cured, the first and second leaf with the elastomer therebetween are separated from the flat surface.
In a particularly preferred manufacturing method, a frame having a plurality of aligned pairs of leaves is formed. Each of the aligned pairs includes a first leaf of flat metal and a second leaf of flat metal having a gap therebetween, and the gaps associated with the aligned pairs are aligned along a straight line. The frame is then translated relative to an application tip that applies flowable elastomer along the straight line. Automated pick and place machinery is then optionally used to affix mirrors and magnets to selected leaves while they are still in the frame. After the elastomer has cured, finished hinge elements are removed from the frame by detaching the leaves from frame runners along the edges of the frame.
In accordance with a still further aspect, the present invention is directed to a chassis for use in forming a scan element for scanning a light beam. The chassis includes a first moveable leaf that is secured to a first fixed leaf by a first hinge, a second fixed leaf that is adjacent to the first fixed leaf, and a third fixed leaf that is adjacent to the second fixed leaf such that the second fixed leaf is positioned between the first and third fixed leaves. The first, second and third fixed leaves are formed from a single sheet of flat metal having first and second bending grooves. The first bending groove separates the first fixed leaf from the second fixed leaf, and the second bending groove separates the second fixed leaf from the third fixed leaf. In order to configure the chassis to scan a light beam in one-dimension, a first mirror is affixed to the first moveable leaf and a second mirror is affixed to the third fixed leaf. In accordance with a further embodiment useful for two-dimensional scanning, the chassis further includes a second moveable leaf coupled to the third fixed leaf by a second hinge, wherein the second hinge has an axis that is perpendicular to an axis of the first hinge. In this further embodiment, a first mirror is affixed to the first moveable leaf and a second mirror affixed to the second moveable leaf.
In accordance with a still further aspect, the present invention is directed to a method for actuating a hand-held portable scan system with force supplied by a user of the system. In this method, a user holds a hand-held portable scan system in the user""s hand. The scan system includes a scan element with a mirror that pivots about an axis. The user then depresses (with the user""s finger or thumb) a switch on a housing of the portable scan system. Energy associated with movement of the user""s finger or thumb during depression of the switch supplies a mechanical impact force to the scan element that causes the mirror to pivot about the axis. In one embodiment, the switch is a mechanical tactile switch.
In accordance with yet a further aspect, the present invention is directed to a method for actuating a scan system using a single non-periodic actuation pulse. A moveable fixture having a mirror and a magnet affixed thereto is provided. The moveable fixture pivots about an axis. A laser that directs a light beam at the mirror is also provided, and a coil is positioned proximate to the magnet. The coil is energized with a single non-periodic pulse of dc current. The single non-periodic pulse results in the application of a distortion force to the magnet that is sufficient to cause the mirror to scan the light beam through a scan angle range that is large enough to illuminate a bar code symbol. The pulse is preferably on the order of about 10-20 milliseconds in duration, and preferably functions to pull the magnet to the coil.
In accordance with a further aspect, the present invention is directed to a method for reading a bar code symbol using scan oscillations that gradually diminish in amplitude. In this method, the bar code symbol is illuminated with a scanning light beam during a plurality of oscillation cycles of the scanning light beam. The scanning light beam has an angular scan range that gradually diminishes with each successive one of the plurality of oscillation cycles. While the scan range of the oscillation cycles is diminishing, reflected light is received from the bar code symbol, and then converted to an electrical signal that is used to decode the bar code symbol.
In accordance with a further aspect, the present invention is directed to a low energy method for actuating a scan system. The scan system includes a moveable fixture having with a mirror affixed thereto, wherein the moveable fixture pivots about an axis, and a laser that directs a light beam at the mirror. A distortion force is applied to the moveable fixture at a first time associated with actuation of the scan system by a user. The distortion force may be supplied from a magnetic coil that is pulse upon actuation of the system. Alternatively, depression of a tactile switch by the user may result in the application of a mechanical distortion force to the moveable fixture. The laser is turned on for a predetermined period of time that expires after the first time, and the laser off is turned off at the expiration of the predetermined period of time. The laser remains on during the predetermined period of time and is turned off at the expiration of the predetermined period of time irrespective of whether a bar code symbol is successfully decoded during the predetermined period of time.
In accordance with still another aspect, the present invention is directed to incorporation of the novel articulated scan elements of the present invention into very compact housings such as those shaped like a pen or a card like a PCMCIA computer card, and the integration of such a scanner into portable hand hold able data collection terminals.